Are mini-implants more effective than traditional anchorage in patients with severe maxillary dentoalveolar protrusion?

When treating patients with severe maxillary dentoalveolar protrusion, clinicians are challenged by the need to retract and/or align the maxillary anterior teeth while preventing molars from moving mesially after extraction of first or second premolars. Some traditional methods of reinforcing anchorage (that is, keeping molars from moving more than the incisors and canines) are use of a Nance holding arch, headgear, and a transpalatal arch fixed to the first and/or second molars. However, several disadvantages are associated with these methods, such as complicated designs and, if headgear is used, the need for exceptional patient cooperation.

To compare the effectiveness of mini-implants with conventional anchorage reinforcement methods in patients with maxillary dentoalveolar protrusion, the authors conducted a systematic review of the literature. Two researchers independently searched electronic databases—PubMed, OvidSP, the Cochrane Library, Chinese Biomedical Literature Database, VIP China Science and Technology Journal Database, Wanfang Data, and China National Knowledge Infrastructure—for retrospective or prospective randomized controlled trials (RCTs) and clinical controlled trials (CCTs) published from December 1966 through March 2016. The study findings are published in the March issue of The Angle Orthodontist.

The systematic review consisted of 14 studies, including 8 RCTs and 6 CCTs. The quality of the 8 RCTS was high, according to standards in the Cochrane Handbook for Systematic Reviews of Interventions. The 6 CCTs received B grades for quality.

All studies were conducted in patients older than 14 years with maxillary or bimaxillary dental protrusion who required extraction of premolars followed by anterior segment retraction with maximum anchorage. The authors explained that for patients who received mini-implants (temporary anchorage devices) during the period of anterior tooth retraction, the mini-implants were screwed into the buccal alveolar bone between the maxillary second premolars and first molars. To be eligible for inclusion, study authors also had to have performed a lateral cephalometric analysis of dental and skeletal movements.

The investigators evaluated 8 aspects of anchorage effectiveness: maxillary incisor distal retraction, mesial maxillary molar movement, axial inclination of the maxillary central incisors to the sella nasion (SN) cranial base plane (U1-SN), angle between the SN plane and the NA plane (SNA angle is a measure of maxillary prognathism), inclination of the mandibular plane to the cranial base, upper lip to the esthetic plane in millimeters (the esthetic plane is a line from the tip of the nose to the tip of the chin), nasolabial angle, and soft-tissue facial convexity measured from glabella to subnasale to soft-tissue pogonion.

Regarding maxillary incisor retraction, the weighted mean difference (WMD) between the 2 groups was –1.50 mm (95% confidence interval [CI], –1.84 mm to –1.17 mm) (P < .00001). More retraction occurred in the mini-implant group than in the traditional anchorage group. For mesial maxillary molar movement, the WMD between the mini-implant and traditional anchorage groups was –2.01 mm (95% CI, –2.45 mm to –1.58 mm), a statistically significant difference (P <. 00001). Therefore, the mini-implant group experienced less mesial maxillary molar movement and less anchorage loss than the traditional anchorage group. The authors pointed out that even “1 mm of [mesial] maxillary molar distal movement has a negative effect on treatment.”

The investigators concluded that mini-implant anchorage was more effective than traditional anchorage in retracting the anterior teeth and preventing anchorage loss in patients with significant maxillary protrusion. Mini-implants and conventional anchorage were equally effective in decreasing U1-SN and SNA (that is, uprighting the central incisors). The variability in findings regarding soft-tissue parameters led the researchers to recommend that more qualified RCTs be conducted.

Editor’s note: The articles in this newsletter address everyday issues in orthodontic practices. The first examines temporary anchorage devices, which are increasingly used in orthodontics to achieve enhanced results over historically used techniques. The second addresses factors that influence the quality of orthodontic treatment outcomes, providing information from a large group of patients treated in a clinical setting. The final 2 articles reflect on long-term orthodontic treatment stability and the use of fixed lower bonded retainers. The authors point out that once active retention ceases (that is, retainers are removed), changes in tooth position are the rule, not the exception.

Assessing factors that may determine excellence in orthodontic treatment

The goal of orthodontic treatment is to achieve excellent outcomes for patients. However, few large studies have investigated the factors that may determine excellence. In this retrospective study, the authors compared patients with excellent orthodontic treatment results with those with unacceptable results with respect to possible prognostic factors. The results were published online March 24 in the European Journal of Orthodontics.

Patients who completed orthodontic treatment from 2003 through 2009 in the Department of Orthodontics at the Justus-Liebig University in Giessen, Germany, with an excellent or unacceptable outcome were included in this retrospective study. Two experienced orthodontists assessed orthodontic treatment outcome according to the Ahlgren index. Of 1,653 patients who met the study’s inclusion criteria, 226 (13.7%) were evaluated as having an excellent outcome and 56 (3.4%) had an unacceptable outcome at the end of the supervised retention period. The remaining patients had a good or an acceptable orthodontic treatment outcome.

According to the Ahlgren index, an excellent outcome is a normal occlusion, as close to Angle’s ideal Class I canine and molar occlusion as possible. An unacceptable outcome is one in which malocclusion remains or has deteriorated or a new malocclusion has developed. Because the Ahlgren index consists of additional subjective factors, the authors also used objective descriptors.

The researchers assessed patients’ lateral cephalograms before treatment (T1) and after the retention period (T2). In addition, they made the following measurement from patients’ plaster casts obtained at T1 and T2: overjet, overbite, sagittal first molar occlusion, and transverse occlusion. Using a special caliper, 2 observers also measured the plaster casts according to the Peer Assessment Rating (PAR) index. (The PAR index is an internationally used measure that provides a single score indicating how far a patient’s dental occlusion and tooth alignment deviate from normal. It measures malocclusion on all 3 spatial planes based on 8 components that are weighted to obtain the overall score.)

Among the study findings, the distribution of male and female patients differed between the excellent and unacceptable treatment outcome groups. Of the 282 patients in the study, 137 (48.6%) were male and 145 (51.4%) were female. However, only 101 (44.7%) of the 226 patients in the excellent outcome group were male, while 125 (55.3%) were female. Of the 56 patients in the unacceptable outcome group, 36 (64.3%) were male and 20 (35.7%) were female. According to the authors, the reason for female predominance in the excellent outcome group is unknown.

The pretreatment PAR index scores did not differ between patients in the excellent and unacceptable outcome groups, providing proof of the comparability of the 2 groups before orthodontic treatment. However, the posttreatment PAR scores were significantly lower (P < .001) in the excellent group than in the unacceptable group. The pretreatment open bite or open bite tendency was more common in the unacceptable group than in the excellent group (44.6% versus 26%), whereas pretreatment deep bite (open bite, > 3.5 mm) was slightly more common in the excellent group (55.3% versus 42.9%).

The study findings showed that the type of orthodontic functional appliance used to correct anteroposterior occlusal discrepancies significantly influenced the treatment outcome. Fixed functional appliances, such as a Herbst appliance, a fixed mandibular anterior repositioning appliance, or fixed interarch springs, reduce the need for patient cooperation compared with the use of removable functional appliances. In the excellent outcome group, 16.4% of patients were treated with fixed functional appliances with multibracket appliances, whereas only 5.5% of those in the unacceptable group were treated with this type of appliance. In addition, 21.4% of patients in the unacceptable group declined treatment with the recommended appliance and chose an alternate plan or underwent premature removal of their appliances.

Patients in the unacceptable outcome group exhibited less cooperation (for example, poor oral hygiene, broken appliances) than patients in the excellent outcome group (P < .001), as indicated by entries in their dental records. According to the authors, lack of cooperation is a “major obstacle in achieving treatment objectives.”

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Achieving long-term stability of orthodontic treatment remains a challenge for clinicians. In this retrospective study, the authors evaluated medium- to long-term treatment stability and assessed the variables that may be associated with it. The findings are published in the March issue of The Angle Orthodontist.

The researchers selected the study sample from a review of posttreatment medical records of patients from a private orthodontic practice and an orthodontic teaching unit at the University of Valencia dental clinic in Valencia, Spain. Inclusion criteria were treatment with fixed appliances, availability of a complete dental and medical record, and casts made at the start and end of treatment, as well as during the follow-up period. They excluded patients who experienced early retainer debonding.

A total of 325 patients met the inclusion criteria, and the authors randomly chose 70 to participate. Of the 70 patients, 46 were female and 24 were male, and their mean age was 14.5 years at the start of treatment. The mean active treatment period was 2.4 years, and 69% of patients did not undergo premolar or incisor extractions. The mean retention phase was 3.3 years, and 70% of patients were treated by means of fixed retention.

To measure treatment stability, the researchers used the Peer Assessment Rating (PAR) index, a comprehensive index that measures malocclusion on all 3 spatial planes based on 8 components that are weighted to obtain the overall score. One orthodontist, who was calibrated against a criterion standard (an orthodontist experienced in using the PAR index), obtained all cast measurements at 3 time points: T1, initial or pretreatment; T2, the end of treatment; and T3, 4 to 10 years after the end of treatment.

The investigators obtained 3 variables from the PAR values: degree of improvement, quality, and stability. They divided improvement into 3 categories: improved—the PAR index value was reduced by fewer than 22 points, the percentage change was greater than 30%, or both; greatly improved—the PAR index value was reduced by at least 22 points, the percentage change was greater than 70%, or both; and worse—no difference—the PAR index value was reduced by less than 30%. Quality was rated high when more than 70% of patients experienced improvement (> 40% of whom must have had great improvement, and no more than 5% of cases could have worsened). Stability was defined as “absolute” when no difference was found between the T2 and T3 PAR index values. When the differences in PAR index values were within ± 5 points, stability was considered “relative.” Differences of more than ± 5 points were classified as “instability.”

The mean pretreatment PAR index value (T1) was 29.8, and the mean PAR index value at the end of treatment (T2) was 6.3. The authors explained that the values at the end of treatment (T2) for this sample of patients met the criteria for a high standard of orthodontic treatment. The difference between the T2 and T3 PAR values was –0.39, indicating a slight worsening in stability. At T3 (4 to 10 years after treatment ended), only 7.1% of the sample exhibited absolute stability, 68.6% displayed relative stability, and 24.4% exhibited instability. The presence or absence of third molars at T3 was not a predictive variable for stability.
The study findings show that lower anterior segment alignment and overbite were overall the most unstable postorthodontic treatment occlusal features (from T2 to T3, 28.6% and 28.5% of cases, respectively, worsened). A “fixed retainer was a protective variable, and the number of years without [fixed or removable] retention was linked to a risk of [lower incisor alignment] instability,” wrote the authors.

Comparing the effectiveness of 2 types of fixed retainers 9 years after their removal

Bonded lingual retainers are often used in orthodontic treatment for retention of mandibular incisors. In this study, published in the March issue of The Angle Orthodontist, researchers compared the long-term effectiveness of 2 types of fixed retainers 9 years after their removal.

The study sample included 64 children (23 boys, 41 girls) who had undergone orthodontic treatment from 1980 through 1995 for Class II malocclusion, deep bite, crowding of the maxillary and mandibular incisors, or any combination of these. The children had received fixed edgewise appliances in both arches. The researchers divided the participants into 2 groups. Group 1 included 28 children who had received a canine-to-canine retainer (0.028-inch stainless steel wire) bonded lingually to the canines. Group 2 included 36 children who had received a 0.0195-inch twistflex retainer bonded lingually to all mandibular incisors and canines. All retainers were custom-made and bonded with composite.

Using a sliding digital caliper, 1 author made all registrations and obtained all measurements on dental casts. The author obtained the measurements at 4 time points: T0, before orthodontic treatment; T1, immediately after treatment (that is, at the start of retention); T2, 6 years after treatment; and T3, 12 years after treatment. The mean length of retention was 2.6 years for patients in the canine-to-canine stainless steel retainer group and 3.0 years for those in the twistflex retainer group. At T3, most patients were 25 through 30 years of age.

The researchers measured several variables, including the irregularity index according to Little (LII) (the summed displacement of the anatomic contact points of the mandibular anterior teeth), intercanine width, intercanine perimeter distance, available mandibular incisor space, 2 measures of lateral arch length, overjet, and overbite. At T0 and T3, they also measured the tooth width of the mandibular incisors. They used lateral head radiographs to evaluate sagittal and vertical relationships between the jaws, incisor inclination, and mandibular length.

Before treatment, mean LII was 4.5 millimeters for patients in group 1 and 4.7 mm for those in group 2. After orthodontic treatment, mean LII was 1.9 mm in group 1 and 1.6 mm in group 2. However, 9 years after retention, mean LII was 4.2 mm in group 1 and 4.4 mm in group 2, indicating a significant increase in mandibular incisor crowding and loss of space.
Overjet and overbite were reduced after orthodontic treatment in both groups and remained fairly stable during the observation period. In addition, the study’s results showed no difference in mandibular incisor stability between patients who underwent tooth extractions before orthodontic treatment and those who did not.

The authors concluded that the retention methods were equally effective during the retention period; thus, both can be recommended. However, neither the canine-to-canine retainer nor the twistflex retainer prevented long-term changes in mandibular incisor irregularity or available space for the mandibular incisors once the fixed retainers were removed.

Dental practice management expert Ginny Hegarty discusses what dental leaders can learn from the Academy Awards mishap in March and why it’s best for you, your team and your patients to establish a cell phone policy.

The Spring 2017 issue of Dental Practice Success also features articles on preparing for retirement, mapping your move from dental school to practice, branding basics, and much more.

News You Can Use

DOS offers ‘once in a lifetime opportunity’ for children in need

The American Association of Orthodontists (AAO) sponsors Donated Orthodontic Services (DOS), a program to provide orthodontic care to low income children who lack insurance coverage or who do not qualify for other assistance in their states of residence.

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